Spitfire engine swaps

[DanMi]

12 hours ago, Nigel Clark said:

The HS2 carbs were good for 75bhp on the Spit Mk3 (and incidentally, a pair of HS2s delivered the same power output on the 1275cc Mini Cooper S). The Spit Mk4 in standard form makes only 63bhp

Those power outputs are true but not really a fair comparison. The MK3 was measured without ancillaries eg dynamo, water pump etc. the mk4 with. The early mk4 actually produced the same power as the mk3, the only real difference being larger crank journals. The later mk4 was slightly lower as it had a milder cam

[rlubikey]

I would have thought small carbs favoured torque due to the increased gas speed at lower revs. They would only be marginal for top-end power which doesn't suit MJH2454's driving style.

You might get a small increase in torque by changing to a single carb and Triumph's "log" manifold. This was tested by John Thomason (also John Kipping??) and gave better economy and a little more torque for a small loss of max revs power. Thomason tried this on a 1500cc Spitfire, but I imagine the same would apply to a 1300 engine.

The simplest swap is a complete 1500 engine. Hoist it in and you're done. You might be able to modify your existing 1300 but I can't say if this is simply a crank swap or you need new con rods & pistons as well. Could you use the same head? Someone will be along shortly to say if the compression will be up the creak!

As mentioned, you can stroke the engine to 1700 (actually, isn't it about 1650cc??) with an offset grind on a 1500 crank, 1300 small bearing rods and TR5 pistons. Loads of torque!

Any of the 6 cylinders will give more torque, but as has been said you have a massive chunk of weight added in front of the front axle which changes the nature of your car. You can do an engine-back 6-cylinder installation, but this requires a lot of engineering and time to do yourself, or very deep pockets for a professional job! You do end up with a nicely balanced car. Triumph never did one because, I believe, it would have embarrassed TR6 owners!

One more thing, Triumph used a wide-ratio gearbox on their stroked engines. I think they knew that this suited the torque of these units. They matched this with a lower ratio diff such as 3.63 or 3.27 (small-chassis) or 3.89 or 3.47 (saloon & TRs).

I think I've remembered all these right, but please correct me if I've got something wrong.

Cheers, Richard

[Iain T]

Can you fit a TR3 or 4 engine in a spitfire? Lots more torque and power but I assume would require a lot of mods. My TR3A had lots of low down torque.

Iain

[rlubikey]

If you think a Triumph 6-cylinder is heavy, the wet-liner from the earlier TR's is REALLY heavy. Oh, and it's BIG. Does someone have the figures to hand?

[Iain T]

I've been searching and I think a big bonnet power bulge would be required as the TR2-4 engine is tall.

I had a Spitfire 1500 and it was nice but slow. Personally although expensive I would go for a 1500 with 2 (or perhaps 1) Genvey Heritage throttle bodie(s), trigger ignition, torque cam profile and sort the head and manifold. A nice (expensive) but controllable and tunable option.

Iain

[MJH2454]

On 30/07/2024 at 19:10, Nigel Clark said:

Had you considered staying with your present engine and giving it a few tweaks? The Mk4 1300 isn't the most powerful Spitfire engine but it will respond well to a slightly hotter camshaft e.g. from the Mk3, plus a stage 2 head and suitable needles in the carbs.

Nigel

I like this idea, Canley Classics offer a modified cam aimed at the larger crank MKIV models, can you offer any pointers to what needles to start looking at with these mods? 

[DanMi]

The Canley classics cam is a mk3 grind on a large journal camshaft, so the early mk4 needles would be correct as they used the same cam as a mk3 would be a good stating point, a late mk4 already has a bigger valve head so AAN which I believe is the same as you have already

Edited August 3 by DanMi

[rlubikey]

Some time ago I downloaded a 1300/1500 engine comparison from a forum. I can't remember the forum and I don't know which publication it came from - does anyone recognise it?

Assuming the details are accurate, it says that the Mk3 and early Mk4 had the same cam, compression and valves, but the Mk4 was down on power and torque**. Later Mk4s got the power back but lost even more torque**. Triumph achieved this using a new cam, larger inlet valves and higher compression.

EDIT: Of course the later Mk4 was even more down on POWER but got the TORQUE back. I read the columns the wrong way round - what a ninny!

**All this is clouded somewhat by the fact that power and torque quoted on earlier cars was Imperial (an optimistic measure with ancillaries removed) whereas later ones are DIN (more realistic and therefore lower). The changeover was somewhere around 1971 or '72 - does anyone know?? So some figures such as Mk3 will be Imperial while the 1500 is DIN. What are the early and late Mk4 figures - Imperial or DIN???

Cheers, Richard

Edited August 3 by rlubikey

[DanMi]

I think that the mk3 was imperial the mk4 din hence the lower quoted power output when the engines were tuned the same bar a heavier crank and swing needles in the carbs. The Mk4 was slightly slower on acceleration but was a bit heavier and had a higher ratio final drive. Probably the MK4 was the first to use din and all models from then on used Din

Edited August 3 by DanMi

[cliff.b]

I have a 1500 Spit and had an earlier MkiV in the past. I find the 1500 has considerably more torque, to the point where you can be in top gear at little more than tick over then smoothly pull away. No need to change down for 20mph villages or, if driving sedately, bends on winding B roads. Obviously need to use the gears if driving more enthusiastically but even then, doesn't seem much point in exceeding 5000RPM as the revs will still be in the right range after you change up and going higher doesn't really seem to aid progress much. 

[MJH2454]

On 05/08/2024 at 12:16, cliff.b said:

I have a 1500 Spit and had an earlier MkiV in the past. I find the 1500 has considerably more torque, to the point where you can be in top gear at little more than tick over then smoothly pull away. No need to change down for 20mph villages or, if driving sedately, bends on winding B roads. Obviously need to use the gears if driving more enthusiastically but even then, doesn't seem much point in exceeding 5000RPM as the revs will still be in the right range after you change up and going higher doesn't really seem to aid progress much. 

Hi Cliff, well I have bitten the bullitt and got my hands on a 1500 engine for rebuilding, it's the torque I'm after, as my original post, I rarely rev my 1300 beyond 3000rpm, peak torque of the 1500 is around 3000rpm job done. When I rebuild, just cos I can, I'm going for a MK3 profile cam and stage 2 head for just a little bit more torque and bhp. If Mark gets back in the groove again maybe we'll meet up again on one of his runs.

[cliff.b]

6 hours ago, MJH2454 said:

Hi Cliff, well I have bitten the bullitt and got my hands on a 1500 engine for rebuilding, it's the torque I'm after, as my original post, I rarely rev my 1300 beyond 3000rpm, peak torque of the 1500 is around 3000rpm job done. When I rebuild, just cos I can, I'm going for a MK3 profile cam and stage 2 head for just a little bit more torque and bhp. If Mark gets back in the groove again maybe we'll meet up again on one of his runs.

Yes, not sure what Mark is up to at the moment but I'm missing the drives out.

[sulzerman]

My mk1V has a standard 1500 dolomite engine fitted with HS4 SU carbs, overdrive and a mk1V diff. It runs very well with 46mpg on a run, I'm very pleased.

I can't compare to a 1300 as I have never driven one